Portrayed as the arch-villain of this decade (Laurence et al., 1988), the drunk driver has increasingly become an intolerable part of our culture. Producing over one million annual drunk driving arrests and accounting for over 25,000 deaths each year in the U.S., drinking and driving presents a serious problem for society in general, and more particularly, for our legislative system. Burdened with the responsibility of providing legal remedies to deter drunk driving, judges in many states are currently sentencing those convicted of DUI to use in-vehicle alcohol test devices (ignition interlock systems) as a condition of probation. In most cases, interlocks are ordered in lieu of license suspension, but in addition to fines, jail sentences, and rehabilitation programs. Although there are currently hundreds of offenders using interlock devices, with the numbers expected to grow as additional states pass legislation authorizing their use, there is no sound empirical evidence to date that it is, in fact, effective in reducing recidivism. Further, virtually nothing is known about the operational characteristics of the device, the attitudes and perceptions surrounding its use, and the concurrent and long-term attitudinal or behavioral effects that can be attributed to the device. The primary objective of this three year study is to evaluate the short and long term effectiveness of interlock systems used in the sentencing of DUI offenders as a deterrent to a subsequent arrest for DUI. Short- term effects are those observed during the period the interlock system is operational in the cars of experimental group members and drivers' licenses are suspended for control group members; long-term effects are those observed over a one year period after the interlock equipment has been removed from the cars of the experimentals, and drivers' licenses are reinstated for the controls. The design of the study involves a quasi-experimental design with precision matched experimental and control group members convicted of DUI, four waves of data collection involving personal face-to-face interviews and police record searches for DUI rearrest. The results of this study, the first comprehensive study of interlock devices known to the investigators, will have direct policy implications both for states passing formal legislation authorizing judges to use this equipment in DUI sentencing and for local judges using interlock programs.